Relative position detection device for motor vehicle

ABSTRACT

A relative position detection device is designed with multiple Hall Effect sensors. In one embodiment, the multiple Hall Effect sensors comprise two different types of Hall Effect sensors. The two different types can be linear and digital. The output of the sensors is used to determine the position an accelerator control, such as a twist grip, and to control an engine or motor in accordance with the operator demand evidenced by the position of the accelerator control.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2004-299,519, which was filed on Oct. 14, 2004, which application ishereby expressly incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a relative position detectiondevice capable of detecting a reference position of a first member and asecond member that are displaceable relative to each other. Moreparticularly, the present invention relates to a straddle-type vehiclein which a drive device, such as a motor or an engine, is controlledusing the relative position detection device.

2. Description of the Related Art

In the motorcycle art, an accelerator grip is rotationally mounted on ahandlebar and the accelerator is rotated with respect to the handlebarto open and close a throttle valve of the internal combustion engine. Onmany motorcycles, an electric relative position detection device isused, in which the rotational movement of the accelerator is detected bya potentiometer and the throttle valve is opened and closed by anactuator based upon the output voltage from the potentiometer.

To reduce the likelihood of a malfunction in the potentiometer resultingin undesired throttle positional control, a separate mechanical switchalso is provided that is capable of detecting a completely-closedposition of the accelerator so as to close the throttle valve if theaccelerator is positioned in the closed position and the throttle valveis not fully closed.

An improved system also has been developed that features a magneticrelative position detection device in which a magnet is disposed in anaccelerator and the rotational position of the accelerator is detectedvia changes in the magnetic flux density. In addition, a furtherimproved system makes use of a Hall Effect sensor.

For example, in JP-A-Hei 7-324637, for the purpose of detecting therotational position of the accelerator so as to control ignition of theinternal combustion engine, a magnet is fixed to an accelerator, twodigital Hall Effect sensors are secured to the handle and it is judgedwhether the accelerator is in the idling range, the middle-speed rangeor the high speed range. Nevertheless, detection of the amount ofrotation of the accelerator necessary to control the opening and closingof the throttle valve still is performed using a potentiometer or thelike. Moreover, because the magnet is relatively small, if theaccelerator grip is rotated, the gap between the magnet and the HallEffect sensor grows to such a degree that the magnetic flux densityexerted on the Hall Effect sensor become very small. Thus, if a magneticforce is present in the vicinity of the sensor, the outside magneticforce can result in improper operation of the system.

Further, FIG. 2 of JP-A-2002-256904 disclosed a relative positiondetection device in which a permanent magnet is fixed to an acceleratorand two Hall Effect sensor that function in the same manner as eachother are fixed to a housing fastened to a handle shaft. In this case,although the details are not clear, an electric signal is output inresponse to the position of the permanent magnet during rotation of theaccelerator using two similarly functioning Hall Effect sensors.

However, since in a relative position detection device using aconventional potentiometer, the potentiometer is larger than anaccelerator, the potentiometer is more likely to degrade the aestheticsof the vehicle if the potentiometer is disposed around the accelerator.Therefore, it usually is disposed at a position other than around theaccelerator and is connected to the accelerator with a conductive wireor the like, which is likely to increase the number of parts,human-hours required for assembling and the like. In addition, overtime, the conductive wire is likely to elongate over time and,therefore, increases the need for maintenance.

SUMMARY OF THE INVENTION

One aspect of the present invention involves a relative positiondetection device comprising a first member. A second member is capableof displacement relative to the first member. The first member comprisesa magnetic portion. The magnetic portion generates a magnetic field. Thesecond member comprises a first Hall Effect sensor. The first HallEffect sensor is positioned within the magnetic field. The first HallEffect sensor is adapted to output a detection signal of a referenceposition from a flux density of the magnetic field generated by themagnetic portion. The magnetic portion comprises an S-pole section andan N-pole section that are arranged along the first member side by sidein the direction of the relative displacement. The first Hall Effectsensor is configured to sense the flux density of the magnetic field atall times throughout a range in which the first member and the secondmember displace relative to each other.

Another aspect of the present invention involves a relative positiondetection device comprising a first member mounted to a handlebarassembly. The first member comprises a magnetic portion. The magneticportion generates a magnetic field. A second member also is mounted tothe handlebar assembly. The second member comprises a detecting portion.The second member comprises means for detecting relative movementbetween the first member and the second member and outputting areference position signal.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will now be described with reference to the drawings of apreferred embodiment, which embodiment is intended to illustrate and notto limit the invention. The drawings comprise 7 figures.

FIG. 1 is a plan view, partly in section, of an accelerator combinedwith a relative position detection device that is arranged andconfigured in accordance with certain features, aspects and advantagesof the present invention.

FIG. 2 is a sectional view of the device of FIG. 1, taken along lineA-A.

FIG. 3(a) is a longitudinal sectional view of the accelerator and FIG.3(b) is an end view of the accelerator taken along the line B-B of FIG.3(a).

FIG. 4 is a perspective view of a split housing member of the device.

FIG. 5 is a plan view of a detection section of the device.

FIG. 6 is a sectional view, showing the relationship between the endportion of the accelerator and the detection section of the device.

FIGS. 7(a) through 7(d) are graphical representation, in which FIG. 7(a)shows a change in flux density at the position of a digital Hall Effectsensor, FIG. 7(b) shows a change of a first detection signal, FIG. 7(c)shows a change in flux density at the position of a linear Hall Effectsensor, and FIG. 7(d) shows a change of a second detection signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference now to FIG. 1 through FIG. 8, a device that is arrangedand configured in accordance with certain features, aspects andadvantages of the present invention is illustrated. In oneconfiguration, the device is applied to an accelerator of a motorcycle.The device, however, can be applied to any number of other vehicles,including but not limited to go-karts, four wheel vehicles, watervehicles, scooters and the like.

The illustrated device comprises a twist grip 11, which can be used tocontrol throttle position or the output of an associated drive member,such as an engine or an electric motor, for example but withoutlimitation. Thus, the twist grip 11 can also be termed an accelerator.

The illustrated twist grip 11 generally defines a first member, which ismounted for rotation on a handlebar 10 near one end of the handlebar 10.A housing 12 generally defines a second member, which also can be fixedto the handlebar 10. In the illustrated configuration, the housing 12 issecured to the handlebar 10 at a position generally corresponding to atube guide section 11 a that is connected to, or forms a portion of, thetwist grip 11 in the illustrated embodiment.

With reference to FIG. 1 and FIG. 2, the tube guide section 11 apreferably is located laterally inwardly of the balance of theaccelerator 11. The tube guide section 11 a of the accelerator 11 iscontained in the housing 12 and is preferably mounted such that it canrotate relative to the housing 12.

With reference still to FIG. 2, a detection section 13 also is disposedinside the housing 12. In the illustrated configuration, the detectionsection 13 is positioned opposite the tube guide section 11 a of theaccelerator 11. The detection section 13 is adapted to detect movement(e.g., an opening) of the accelerator 11. Wires 13 a for the detectionsignal extend from the detection section 13 and connect to a controlsection 14. The control section 14 can be mounted in any suitablelocation on a vehicle, such as on a body component of the vehicle, forexample but without limitation. Another wire 14 a preferably extendsfrom the control section 14 to a throttle device 16 or the like. Whilethe throttle device 16 can be in the form of a throttle body for aninternal combustion engine, the throttle device also can be a controldevice that varies the output of an electric motor or the like. Acontrol signal from the control section 14 can be used to manipulate thethrottle device 16 such that the output of the power source (e.g.,internal combustion engine, electric motor, etc.) of the vehicle can becontrolled from the twist grip 11.

With reference to FIG. 3, the accelerator 11 comprises the tube guidesection 11 a, which is disposed inside the housing 12, and a gripsection 11 b, which is disposed outside of the housing 12. The tubeguide section 11 a preferably has a rotation restriction section 11 cand a magnetic member 17. The rotation restriction section 11 c isdesigned to limit the rotational sweep of the accelerator 11 to apredetermined included angle. In one configuration, the rotationrestriction section 11 c is defined by boss that extends outward from anend of the tube guide section 11 a. In another configuration, therotation restriction section 11 c can be a slot or other type of recess.The magnetic member 17 preferably comprises a magnetic component that isshaped in a generally arcuate shape with its center on a rotational axisL1 of the accelerator 11. The magnetic member 17 may comprise apermanent magnet or may comprise any suitable magnetizable substance. Inone preferred configuration, the magnetic member 17 is embedded in thetube guide section 11 a of the accelerator 11. In another configuration,the magnetic member 17 is secured to a surface of the tube guide section11 a. Other suitable configurations also can be used.

With reference to FIG. 1 and FIG. 2, the housing 12 preferably comprisesa pair of split housing members 12 a, 12 b. The split housing members 12a, 12 b encase at least a portion of the handlebar 10. In oneconfiguration, the split housing members 12 a, 12 b clamp the handlebar10 in position when secured together. The tube guide section 11 a of theaccelerator 11 preferably is mounted for rotation within a chamberdefined by the split housing members 12 a, 12 b.

With reference to FIG. 1 and FIG. 4, a container section 12 c is definedinside the split housing member 12 a by one or more rib-like projectionpieces 12 d. In the illustrated embodiment, the container section 12 cis defined by one rib-like projection piece 12 d and the surroundingwalls of the housing 12. The container section 12 c receives the tubeguide section 11 a of the accelerator 11. Preferably, the projectionpiece 12 d cooperates with the rotation restriction section 11 c on thetube guide section 11 a of the accelerator 11 such that the range ofmotion of the accelerator 11 can be limited. In other words, when therotation restriction section 11 c abuts upon the projection piece 12 d,substantial continued rotational movement of the accelerator in the samedirection is prevented. Thus, the rotation restriction section 11 c andthe projection piece 12 d restrict the movement of the acceleration to aranged defined between a completely-closed position θ0 and a fully-openposition θm.

The detection section 13 preferably is mounted in and around the housingsection 12 c of the split housing member 12 a. The detection section 13detects the flux density of the magnetic field generated by the magneticmember 17. With reference to FIG. 5 and FIG. 6, the illustrateddetection section 13 is configured such that a plate-like circuit board20 is supported on a circuit board holder 18. The circuit board holderpreferably is secured to the split housing member 12 a.

The circuit board 20 comprises a magnetic metal plate 19. The plate 19preferably is embedded in the circuit board 20. The plate 19 can beformed of any suitable material but preferably is formed of iron plateor the like. In some configurations, the circuit board itself can bemade of iron or an iron plate may underlie, or be placed adjacent to,the circuit board. Since the magnetic metal plate 19, which is disposedseparate from and facing the magnetic member 17, is embedded in thecircuit board 20 and the digital Hall Effect sensor 21 and the linearHall Effect sensor 22 are disposed between the metal plate 19 and themagnetic member 17, the flux of the magnetic field formed by themagnetic member 17 can be collected toward the metal plate 19 and theflux density can be more easily detected by the digital Hall Effectsensor 21 and the linear Hall Effect sensor 22 compared with when themetal plate 19 is not provided. At the same time, because the digitalHall Effect sensor 21 and the linear Hall Effect sensor 22 are disposedbetween the metal plate 19 and the magnetic member 17, the magnetic fluxfrom outside of the system is greatly reduced by the metal plate 19 andis less likely to reach the digital Hall Effect sensor 11 and the linearHall Effect sensor 12, which greatly reduces the likelihood of amalfunction or the like.

With continued reference to FIG. 5, the illustrated circuit board 20comprises as a narrow section 20 a, which is advantageously sized andconfigured to be positioned within the housing section 12 c of the splithousing member 12 a, as shown in FIG. 5. A digital Hall Effect sensor21, which defines a first Hall Effect sensor, and a linear Hall Effectsensor 22, which defines a second Hall Effect sensor, are mounted on thenarrow section 20 a opposite to each other in a spaced relation from themagnetic member 17. Other suitable types of sensors also can be used.

With reference to FIG. 6, the magnetic member 17 preferably is formed oftwo magnetic pole sections 17 a, 17 b that are fixed adjacent to eachother in the rotating direction of the accelerator 11. The magnetic polesection 17 a that is disposed forwardly in the direction “A” (i.e., thedirection of movement from a completely-closed position θ0 toward afully-open position θm of the accelerator 11) has an S-pole at the innerside and an N-pole at the outer side, while the magnetic pole section 17b which is disposed rearwardly in the direction “A”, has an S-pole onthe outer side and an N-pole on the inner side. Therefore, theillustrated magnetic member 17 is configured such that the N-pole andthe S-pole disposed in the outer sides of the magnetic pole sections 17a, 17 b in the direction “A” are disposed side by side. Advantageously,mounting the N-pole and S-pole portions of the magnetic member 17 sideby side in the direction “A” results in a strong change in magnetic fluxat the boundary section 17 c.

The digital Hall Effect sensor 21 and the linear Hall Effect sensor 22that are mounted on the circuit board 20 preferably are disposed in thedirection perpendicular to the rotation axis L1 of the accelerator 11.In other words, the sensors 21, 22 are positioned in the rotatingdirection of the accelerator 11 at a suitable distance away from eachother. Of these Hall Effect sensors 20, 21, the digital Hall Effectsensor 21 is disposed at a location generally corresponding to aboundary section 17 c between the N-pole and the S-pole in thecircumferential direction of the magnetic member 17 when the accelerator11 is in a completely-closed state θ0. In one advantageousconfiguration, the accelerator 11 is provided with some mechanical playwhen in the position corresponding to the completely-closed state θ0. Insuch a configuration, the digital Hall Effect sensor 21 preferably ispositioned at a location generally corresponding to the vicinity of theboundary section 17 c and while being slightly more disposed toward theN-pole.

In one configuration, the digital Hall Effect sensor 21 is arranged tosense the magnetic force from the magnet member 17 only when theaccelerator 11 is in a closed position. In a preferred configuration,the digital Hall Effect sensor 21 is arranged to receive the magneticforce from the magnetic member 17 throughout the range of acceleratormovement. By such a placement, the digital Hall Effect sensor 21 isalways influenced by the magnetic member 17 and outside magnetic fieldare less likely to impact performance. When the illustrated accelerator11 is rotated, such as when it rotates from the completely-closed stateθ0 to the fully-open state θm, the flux density at the position of thedigital Hall Effect sensor 21 changes generally in the manner shown inFIG. 7(a) so as to decrease gradually from a position at the N-pole sidein which the flux density is low and increases gradually after passing aposition of an extreme density value.

Further, regarding a first detection signal from the digital Hall Effectsensor 21, a voltage V11 is output from the digital Hall Effect sensor21 when the flux density at the corresponding position is not smallerthan a given threshold T1. Thus, the digital Hall Effect sensor 21 doesnot change its output until the sensed flux density drops below thethreshold T1. Once the sensed flux density drops below the threshold T1,a voltage V10 is output from the digital Hall Effect sensor 21. In oneparticularly preferred configuration, the voltage V10 is substantiallyzero.

The linear Hall Effect sensor 22 preferably is positioned substantiallyas shown in FIG. 6. In such a configuration, the linear Hall Effectsensor 22 is at a position facing the N-pole of the magnetic member 17when the accelerator 11 is in the completely-closed state θ0. Morepreferably, the linear Hall Effect sensor 22 is positioned to generallyface the N pole of the magnetic member 17 when the accelerator 11 is atthe completely-closed position θ0 and to generally face the S pole ofthe magnetic member 17 when the accelerator 11 is rotated to thefully-open position θm. Even more preferably, the linear Hall Effectsensor 22 is positioned within a range of the magnetic member 17 thatallows the change in the flux density to be detected in a generallylinear manner such that the detected flux density changes along asloping line similar to that shown in FIG. 6(d).

When the accelerator 11 is rotated from the completely-closed positionθ0 to the fully-open position θm, the flux density sensed by the linearHall Effect sensor varies in a generally linear manner from a positionof higher flux density on the N-pole side to a position of a lower fluxdensity, as shown in FIG. 7(c). The range of change of the flux densitypreferably is a range that encompasses the completely-closed state θ0and the fully-open state θm, or is a range in which the flux densitydetected when the accelerator 11 is displaced from the fully-open stateθm to the completely-closed state θ0 increases or decreases withoutpassing the position of an extreme value. In the illustrated embodiment,the range of flux density encompasses the two extreme acceleratorpositions.

A voltage V20 preferably is output when the sensed flux density is notsmaller than a given threshold T2 and a voltage V20 that is generallyinversely proportional to the flux density preferably is output when theflux density is smaller than the given threshold T2. In one preferredconfiguration, the voltage V20 is substantially zero.

The output voltages from the two Hall Effect sensors 21, 22 aretransmitted to the control section 14. The control section 14 preferablyis configured such that when the output from the digital Hall Effectsensor 21 is V11 a control signal is output by the control section 14 tothe controller 16. The output control signal preferably sets a drivesource, which can be an engine or an electric motor, to a low speedoperating condition. The control section 14 also preferably isconfigured such that when the output from the digital Hall Effect sensor21 is V10 another control signal is output by the control section 14 tothe controller, which control signal generally corresponds to the outputof the linear Hall Effect sensor 22. In this manner, the control section14 enables the drive source to be operated in a manner that generallycorresponds to the output of the linear Hall Effect sensor 22.

In use, the system controls the output of a drive source. Between thecompletely-closed position θ0 as a reference position and a givenopening θ1, the flux density sensed by the illustrated digital HallEffect sensor 21 is not smaller than the threshold value T1, as shown inFIG. 7(a). Therefore, the first detection signal V11 indicative of thecompletely-closed position θ0 is output from the digital Hall Effectsensor 21, as shown in FIG. 7(b). Because the sensed flux density at theposition of the linear Hall Effect sensor 22 is not smaller than thethreshold T2, as shown in FIG. 7(c), the second detection signal V20corresponding to the completely-closed position θ0 is output from thelinear Hall Effect sensor 22, as shown in FIG. 7(d). These outputsignals from the digital Hall Effect sensor 21 and the linear HallEffect sensor 22 are communicated to the control section 14 through thewires 13 a for the detection signal. Wireless configurations also arepossible. A control signal to stop the power supply to the motor istransmitted to the controller 16 from the control section 14 through thewire 14 a. Again, wireless configurations also are possible.

When the accelerator 11 is rotated a little in the direction “A” tocause the opening to be larger than the first opening θ1, the sensedflux density at the digital Hall Effect sensor 21 becomes larger thanthe given threshold T1 and the first detection signal V10 is output.Simultaneously, in the illustrated embodiment, the sensed flux densityat the linear Hall Effect sensor 22 is larger than the given thresholdT2 and so the second detection signal V20 continues to be output fromthe linear Hall Effect sensor 22. Therefore, the control signaldiscussed above, which directs the controller 16 to stop output from themotor, continues to be supplied by the control section 14.

When the accelerator 11 is rotated further in the direction “A” and theopening becomes larger than the second opening θ2, the sensed fluxdensity at the linear Hall Effect sensor 22 becomes smaller than T2while the first detection signal V10 continues to be output from thedigital Hall Effect sensor 21. The drop in the sensed flux density atthe linear Hall Effect sensor 22 causes the linear Hall Effect sensor tooutput a second detection signal V2θ, which generally corresponds to achange in sensed flux density. The output of the second detection signalV2θ is transmitted to the control section 14. In the illustratedconfiguration, the signal is transmitted through the wires 13 a but awireless configuration can be used. Therefore, a control signalcorresponding to the second detection signal V2θ is output through thecontrol section 14 to the controller 16 and the drive source iscontrolled to generally correspond to the second detection signal V2θ.

When the accelerator 11 is set to a full-open position θm, the sensedflux density at the digital Hall Effect sensor 21 is smaller than thegiven threshold T1 and, therefore, the output continues to be V10. Inaddition, the drive source is set to a fully-open position thatcorresponds to the fully-opened position θm of the accelerator, whichcorresponds to the output signal V2θ from the linear Hall Effect sensor22. When the accelerator 11 is rotated back towards the closed position(i.e., in a direction opposite to the direction “A”) but remains in aposition greater than the opening θ2, the power source is operated tocorrespond to the second detection signal V2θ from the linear HallEffect sensor 22. Once the opening of the accelerator decreases belowθ2, the power source is effectively stopped or returned to an idleposition.

When used on a vehicle, such as a motorcycle, the illustrated devicedescribed above can be used to control engine speed. For instance, whenthe digital Hall Effect sensor 21 outputs the first detection signalV11, which is indicative of the accelerator 11 being in thecompletely-closed position θ0, the control section 14 can output acontrol signal corresponding to the completely-closed position. When thedigital Hall Effect sensor 21 outputs the first detection signal V10,which is indicative of the accelerator 11 opening more than a presetangle, the control section 14 can output a control signal correspondingto the second detection signal V20 that is output from the linear HallEffect sensor 22.

When the accelerator 11 is completely-closed (i.e., in thecompletely-closed position θ0) with respect to the housing 12, if thedigital Hall Effect sensor 21 erroneously outputs the first detectionsignal V10, which indicates an opened accelerator position, instead ofthe first detection signal V11, which indicates a completely-closedaccelerator position θ0, as a result of malfunction or the like, thesecond detection signal V20 indicative of the completely-closed positionθ0 is output from the linear Hall Effect sensor 22. Thus, the controlsection 14 can output a control signal corresponding to thecompletely-closed state regardless of the signal received from thedigital Hall Effect sensor 21. When the linear Hall Effect sensor 22outputs the second detection signal V2θ, which indicates that theaccelerator 11 is opened more than a preset angle, as a result ofmalfunction or the like, a first detection signal V11 indicative of thecompletely-closed position θ0 is simultaneously output from the digitalHall Effect sensor 21 so that a control signal corresponding to thecompletely-closed state is output from the control section 14. Thus, theillustrated system has a built-in redundancy that allows the controlsection 14 to stop the engine regardless of one of the sensors 21, 22failing. Accordingly, in the event of a sensor malfunction, no controlsignal based on the malfunction or the like is output to the controller16, which greatly reduces the likelihood of the power source beingcontrolled in an erroneous manner. In other words, if the first and thesecond member are disposed at the reference position and if no firstdetection signal indicative of the reference position is output from thefirst Hall Effect sensor as a result of a malfunction or the like, oreven if the second detection signal corresponding to the position ofrelative displacement is output from the second Hall Effect sensor as aresult of a malfunction or the like, a control signal corresponding tothe reference position is output from the control section, so that nocontrol signal based on a malfunction or the like is output to thecontrolled object, thereby greatly reducing the likelihood of acontrolled object malfunction.

Through the use of the Magnetic member 17, which coupled for rotationwith the accelerator, together with the two Hall sensors 21, 22, whichare mounted in a non-contact relationship with the magnetic member 17,and the control section 14, output from rotation of the accelerator canbe used to control a throttle mechanism, an electric motor or the like.Moreover, the illustrated configuration can replace a potentiometer orthe like that is used in convention systems. Thus, a relatively low costreplacement can be made for a potentiometer-based unit.

Further, compared with a potentiometer-based system, no member such as apotentiometer having a shape larger than that of the accelerator 11 isrequired and the wires or the like for connecting the accelerator 11 andthe potentiometer are unnecessary, which improves the aesthetics of theassembly. Moreover, the number of parts and human-hours for assemblingthe parts can be reduced because of the lack of large numbers ofmechanical parts. Furthermore, the constructions disclosed herein areless likely to deteriorate over time.

Although in the foregoing embodiment, the digital Hall Effect sensor 21detects the flux density below a threshold at the opening θ1 of theaccelerator 11, and after the condition is reached in which no detectionsignal is output, the accelerator is rotated further to output thedetection signal from the linear Hall Effect sensor 22 after the openingreaches θ2, other configurations can be arranged such that the detectionsignal of the linear Hall Effect sensor 22 is output after theaccelerator 11 reaches a position of the opening θ1 at which subsequentoutput of the detection signal from the linear Hall Effect sensor 22 isstopped. Also, the device can be arranged such that the detection signalof the linear Hall Effect sensor 22 is output at a position where theaccelerator 11 reaches an opening smaller than the opening θ1. In thiscase, control is performed such that the detection value from the linearHall Effect sensor 22 is offset-operated at the position of the openingθ1.

Although the present invention has been described in terms of a certainembodiment, other embodiments apparent to those of ordinary skill in theart also are within the scope of this invention. Thus, various changesand modifications may be made without departing from the spirit andscope of the invention. For instance, various components may berepositioned as desired. Moreover, not all of the features, aspects andadvantages are necessarily required to practice the present invention.Accordingly, the scope of the present invention is intended to bedefined only by the claims that follow.

1. A relative position detection device comprising a first member, asecond member being capable of displacement relative to the firstmember, the first member comprising a magnetic portion, the magneticportion generating a magnetic field, the second member comprising afirst Hall Effect sensor, the first Hall Effect sensor being positionedwithin the magnetic field, the first Hall Effect sensor adapted tooutput a detection signal of a reference position from a flux density ofthe magnetic field generated by the magnetic portion, the magneticportion comprising an S-pole section and an N-pole section that arearranged along the first member side by side in the direction of therelative displacement, and the first Hall Effect sensor being configuredto sense the flux density of the magnetic field at all times throughouta range in which the first member and the second member displacerelative to each other.
 2. The device of claim 1 in combination with ahandlebar, one of the magnetic portion and the first Hall Effect sensorbeing fixed to the handlebar and the other to an accelerator gripmounted to the handlebar for rotation relative to the handlebar, therelative position detection device being mounted in such a manner that acompletely-closed position of the accelerator grip is defined as thereference position.
 3. The device of claim 1, wherein the first HallEffect sensor is a digital Hall Effect sensor.
 4. The device of claim 3further comprising a magnetic metal plate and the first Hall Effectsensor being disposed between the metal plate and the magnetic portion.5. The device of claim 4 in combination with a handlebar, one of themagnetic portion and the first Hall Effect sensor being fixed to thehandlebar and the other to an accelerator grip mounted to the handlebarfor rotation relative to the handlebar, the relative position detectiondevice being mounted in such a manner that a completely-closed positionof the accelerator grip is defined as the reference position.
 6. Thedevice of claim 3, wherein the second member further comprises a secondHall Effect sensor that is adapted to detecting a change of the fluxdensity of the magnetic field generated by the magnetic portion, and thesecond Hall Effect sensor is located in a range within which the fluxdensity of the magnetic field of the magnetic portion changes in agenerally linear manner.
 7. The device of claim 6 in combination with ahandlebar, one of the magnetic portion and the first Hall Effect sensorbeing fixed to the handlebar and the other to an accelerator gripmounted to the handlebar for rotation relative to the handlebar, therelative position detection device being mounted in such a manner that acompletely-closed position of the accelerator grip is defined as thereference position.
 8. The device of claim 3 in combination with ahandlebar, one of the magnetic portion and the first Hall Effect sensorbeing fixed to the handlebar and the other to an accelerator gripmounted to the handlebar for rotation relative to the handlebar, therelative position detection device being mounted in such a manner that acompletely-closed position of the accelerator grip is defined as thereference position.
 9. The device of claim 7 further comprising amagnetic metal plate and the first Hall Effect sensor being disposedbetween the metal plate and the magnetic portion.
 10. The device ofclaim 9 in combination with a handlebar, one of the magnetic portion andthe first Hall Effect sensor being fixed to the handlebar and the otherto an accelerator grip mounted to the handlebar for rotation relative tothe handlebar, the relative position detection device being mounted insuch a manner that a completely-closed position of the accelerator gripis defined as the reference position.
 11. The device of claim 1, whereinthe second member further comprises a second Hall Effect sensor that isadapted to detecting a change of the flux density of the magnetic fieldgenerated by the magnetic portion, and the second Hall Effect sensor islocated in a range within which the flux density of the magnetic fieldof the magnetic portion changes in a generally linear manner.
 12. Thedevice of claim 11 in combination with a handlebar, one of the magneticportion and the first Hall Effect sensor being fixed to the handlebarand the other to an accelerator grip mounted to the handlebar forrotation relative to the handlebar, the relative position detectiondevice being mounted in such a manner that a completely-closed positionof the accelerator grip is defined as the reference position.
 13. Thedevice of claim 11 further comprising a magnetic metal plate and thefirst Hall Effect sensor being disposed between the metal plate and themagnetic portion.
 14. The device of claim 13 in combination with ahandlebar, one of the magnetic portion and the first Hall Effect sensorbeing fixed to the handlebar and the other to an accelerator gripmounted to the handlebar for rotation relative to the handlebar, therelative position detection device being mounted in such a manner that acompletely-closed position of the accelerator grip is defined as thereference position.
 15. The device of claim 1 further comprising amagnetic metal plate and the first Hall Effect sensor being disposedbetween the metal plate and the magnetic portion.
 16. The device ofclaim 15 in combination with a handlebar, one of the magnetic portionand the first Hall Effect sensor being fixed to the handlebar and theother to an accelerator grip mounted to the handlebar for rotationrelative to the handlebar, the relative position detection device beingmounted in such a manner that a completely-closed position of theaccelerator grip is defined as the reference position.
 17. A relativeposition detection device comprising a first member mounted to ahandlebar assembly, the first member comprising a magnetic portion, themagnetic portion generating a magnetic field, a second member alsomounted to the handlebar assembly, the second member comprising adetecting portion, the second member comprising means for detectingrelative movement between the first member and the second member andoutputting a reference position signal.
 18. The device of claim 17,wherein the means is positioned so as to remain within a detectableportion of the magnetic field throughout a range of motion of the firstmember relative to the second member.
 19. The device of claim 17,wherein the magnetic portion comprises an S-pole section and an N-polesection that are arranged along the first member side by side in thedirection of the relative displacement.